Все, что вам нужно знать о LDPE

Looking for LDPE with good chemical stability? LDPE is a plastic material suitable for various thermoplastic molding processes, offering excellent processability.

In this article, we’ll explore everything about LDPE and its applications across industries ranging from pipe manufacturing to everyday consumer goods.

LDPE has a melting point of 120~125°C, between that of HP-LDPE and HDPE, thus exhibiting good flexibility and elongation, but also possessing certain limitations. It has good transparency, cold resistance, and processability; its chemical stability is good, resisting acids, alkalis, and salt solutions; it has good electrical insulation and air permeability; low water absorption; and it is flammable.

When LDPE is heated, as the temperature rises, crystallization gradually decreases until the crystalline portion disappears completely, at which point the polyethylene melts. This temperature is the melting point. As the density of polyethylene increases, its crystallinity also increases, and the melting point rises accordingly. Therefore, polyethylenes with different densities have different melting points. The melting point of LLDPE is 120-125°C, between that of HP-LDPE and HDPE.

The melting point of LLDPE, a copolymer of monomers, varies with the number of carbon atoms in its comonomers; more carbon atoms result in a higher melting point. Because LLDPE has a higher melting point than HP-LDPE, molded products can be demolded quickly and cleanly at higher temperatures. LDPE films have high heat-sealing strength. The fluidity of LDPE at increasing temperature and its changes under increased load are mainly affected by its molecular weight.

Since it is easier to measure the melt flow rate of polyethylene than its molecular weight, the melt index (MI) or melt flow index (MFI) is usually used to represent the molecular weight characteristics of polyethylene. In the molten state, the melt viscosity of LDPE is a function of molecular weight, increasing with increasing molecular weight. For the same molecular weight, melt viscosity decreases with increasing temperature. LDPE densities at room temperature exhibit varying toughness.

Low-temperature LDPE naturally possesses good toughness, with a lower embrittlement temperature, which is related to molecular weight. As LDPE molecular weight increases, the temperature decreases, reaching -140°C. At the same molecular weight, linear LLDPE and HDPE have higher melt viscosities than non-linear LDPE. With the same melt index, LDPE has a significantly lower melt viscosity than LLDPE and HDPE; the former exhibits significantly better melt flow during processing, while the latter two require less screw load and generate less heat.

LDPE grades can meet the requirements of most thermoplastic molding processes, including: film blowing, film casting, extrusion bonding, wire and cable bonding, injection molding, and blow molding.

LDPE is primarily used for film products, such as agricultural films, ground covering films, and greenhouse films for vegetables; packaging films for candy, vegetables, and frozen foods; blown films for liquid packaging (milk, soy sauce, juice, tofu, soy milk); heavy-duty bags, shrink wrap films, elastic films, and inner lining films; construction films; general industrial packaging films; and food bags.

LDPE is also used in injection molding products, such as small containers, lids, daily necessities, plastic flowers, injection-stretch-blow molded containers, medical devices, and pharmaceutical and food packaging materials. Extruded трубы and sheets, wire and cable sheathing, profiles, and thermoformed products are also used. Blow-molded hollow products include food containers for dairy products and jams, and containers and tanks for pharmaceuticals, cosmetics, and chemical products. Calcium-plastic boards and foam plastics are also used. Rotational molding products are mainly used for large containers and storage tanks.

Low-density polyethylene (LDPE) is the lightest type of polyethylene resin. Compared to high-density polyethylene (HDPE), it has lower crystallinity (55%~65%) and softening point (90~100°C); it has good flexibility, extensibility, transparency, cold resistance, and processability; it has good chemical stability, resisting acids, alkalis, and salt solutions; it has good electrical insulation and air permeability; it has low water absorption; and it is flammable. It is relatively soft and possesses good extensibility, electrical insulation, chemical stability, processability, and low-temperature resistance (can withstand -70°C).

The main drawbacks are its poor mechanical strength, moisture barrier properties, gas barrier properties, and solvent resistance. Its molecular structure is not regular, with low crystallinity (55%-65%) and a relatively low melting point (108-126°C). Its mechanical strength is lower than that of high-density polyethylene (HDPE), and it has poor impermeability, heat resistance, and resistance to sunlight aging. It is prone to aging and decomposition under sunlight or high temperatures, leading to discoloration and performance degradation. Therefore, antioxidants and UV absorbers are added when making low-density polyethylene into plastic rolls to improve its shortcomings.

LDPE is a premium plastic material that excels in the pipe industry and can be used to manufacture a wide variety of pipes and everyday consumer goods. Its high strength and excellent properties make it ideal for demanding applications.

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